What this means
The IEEE assigned the MA-L block 68D40C to TELLESCOM INDUSTRIA E COMERCIO EM TELECOMUNICACAO. Every network interface they manufacture under this block has a MAC address beginning with these digits, followed by a unique per-device identifier. If a device on your network shows a MAC starting 68:D4:0C, it is TELLESCOM INDUSTRIA E COMERCIO EM TELECOMUNICACAO hardware.